In a prior art telecommunication switching system comprising a plurality of switching nodes, each switching node requires predefined knowledge of the numbering plan of the telecommunication switching system and also of how the switching nodes are interconnected. An example of such a system is the public telephone network in the United States. Within the United States, the telephones are grouped in terms of area codes; and within each area code, the telephone numbers are further grouped by the first three digits of the telephone number. The telecommunication system itself involves tandem switching systems and central office switching systems. Each central office system is responsible for groups of telephone numbers with each group being specified by the first three digits of the telephone number. This hierarchy of telephone numbers (also referred to as the dialing plan hierarchy) is modeled after the hierarchy of switching nodes, e.g. central and tandem offices. Within each central office, the routes to be utilized to reach area codes or other groups of telephone numbers is predefined at system initialization or during system operation by the actions of a system administrator. Telephones locally connected to a central office must be assigned a number from the predefined block of numbers assigned to the central office. One problem with the prior art is that a new telephone number must be manually assigned to a person every time a person moves by a system administrator at a new central office since the new telephone number must be from the telephone numbers assigned to that central office.
U.S. Pat. No. 4,442,321 discloses a distributed dialing plan in which the dialing plan is distributed to switching systems in a horizontal manner such that each switching system (switching node) occupies the same hierarchical level as any other switching systems. The switching systems are interconnected by links, and a switching system is assigned a block of telephone numbers. To place a call with a dialed telephone number received from a connected telephone, the switching system determines if the dialed telephone number is part of the telephone numbers assigned to the switching system or is part of a block owned by another switching system. This decision is based on the most significant digits of the dialed telephone number. If the dialed telephone number belongs to another switching system, the switching system searches an internal table to determine which link interconnects the switching system to the other switching system and uses that link to route the call to the other switching system. The problem with this distributed dialing plan is that every switching system has to have predefined information defining the blocks of numbers owned by all of the other switching systems.